1. Field of the Invention
The present invention generally relates to malfunction warning systems for watercraft having outboard motors. More specifically, the present invention relates to control units capable of reducing false alarms in lubrication system malfunction detection systems.
2. Description of Related Art
Outboard motors pose unique challenges to engine designers due to their orientation and the rotation of the engines about a tilting and trimming axis during operation. One such challenge involves supplying lubricant to the moving components of the engine during a variety of operating conditions. Because the engine does change in orientation during use, accurately sensing a level of lubricant remaining in an oil pan becomes difficult, if not impossible. Such a measurement is desirable to ensure that the engine is not run dry of lubricant because of a leak or passage clogging.
In some outboard motors, the engine has a pressure sensor that detects a decrease in lubricant by evaluating the operating pressure within the lubrication system. If the pressure falls to a level indicative of a malfunction, then a buzzer or other alarm immediately sounds. One difficulty in such sensors is determining whether the low pressure is indicative of an actual problem or, rather, is indicative of a sudden change in operating conditions. For instance, due to the viscous nature of oil as a lubricant, the pressure of the lubricant does not vary as rapidly as engine speed. Accordingly, upon rapid acceleration, the lubricant pressure may incorrectly indicate a low pressure and a nonexistent malfunction.
Some engine designers have remedied these false alarm problems by setting the sensor to indicate a problem only when the pressure falls below a minimum pressure that corresponds to an adequate supply of lubricant during idle speed operation. Such a setting, however, allows the engine to operate at high speeds with inadequate lubrication, thereby reducing the durability and life span of the engine.
Accordingly, a system is desired that can decrease the number of false alarms while simultaneously protecting the engine during high speed operation.
One aspect of the present invention involves a malfunction detection system for use in a lubrication system of an engine of an outboard motor. The system comprises sensing an engine speed, sensing a rate of change in engine speed, and sensing a pressure in the lubrication system. The system determines if the sensed pressure is below a minimum pressure indicative of a malfunction in the lubrication system and activates an alarm procedure if the sensed pressure is below the pressure indicative of a malfunction in the lubrication system. The system also delays the alarm procedure if the engine is in a period of rapid change in engine speed.
Another aspect of the present invention involves an outboard motor comprising an engine and a lubricant pump powered by the engine. The lubricant pump is capable of pumping lubricant through a lubricant supply passage. Preferably, a pressure sensor is positioned along the supply passage and the pressure sensor is in communication with a control unit. In the illustrated embodiment, the control unit is capable of activating an alarm sequence when the pressure sensor emits a signal indicative of an abnormally low pressure within the supply passage and the control unit delays activating the alarm sequence when the engine is in a period of rapid engine speed change.